Have you tried out using personalization purge. Think it is the global option or main menu one. That controls the the layout custom.
Do users already have a default home page selected in user account security maintenance? Maybe set it to a new one there. We did a main one call MAIN426 (month year). Then released another one called MAIN826 a few months later. Then deleted the old one. DMT’d the user account to the new menu. Maybe what we are doing could also work for you. Your example PURCHASING826
We took away the ability for users to ‘update’ their homepages as we classified ours as Corporate Homepages. We published a load for all departments and if users wanted tiles added it had to be something that was required by everyone. Users soon came round to the idea.